The present invention generally relates to prepolymers based on block copolymers of a silicone-containing material and a hydrophilic material. The prepolymers are useful as a hydrogel lens material, such as a hydrogel contact lens or intraocular lens material.
Hydrogels represent a desirable class of materials for many biomedical applications, including contact lenses and intraocular lenses. Hydrogels are hydrated, cross-linked polymeric systems that contain water in an equilibrium state. Silicone hydrogels are a known class of hydrogels and are characterized by the inclusion of a silicone-containing material. Typically, a silicone-containing monomer is copolymerized by free radical polymerization with a hydrophilic monomer, with either the silicone-containing monomer or the hydrophilic monomer functioning as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable functionalities) or a separate crosslinker may be employed. An advantage of silicone hydrogels over non-silicone hydrogels is that the silicone hydrogels typically have higher oxygen permeability due to the inclusion of the silicone-containing monomer. Because such hydrogels are based on monomers polymerizable by free radical, these materials are thermosetting polymers.
U.S. Pat. No. 5,034,461 (Lai et al.) discloses polyurethane-containing prepolymers. These prepolymers may be copolymerized with a hydrophilic comonomer to form a silicone hydrogel copolymer that is useful as a contact lens material and other biomedical device applications. The prepolymers exemplified in U.S. Pat. No. 5,034,461 do not include any major hydrophilic portion, and therefore, these prepolymers are copolymerized with a hydrophilic monomer to form a hydrogel copolymer.
This invention provides a prepolymer useful as a hydrogel material, represented by the formula (I): ##STR2##
wherein PA1 M is a hydrophilic radical derived from at least one hydrophilic ethylenically unsaturated monomer and having a molecular weight of about 500 to 5000; PA1 each R is independently selected from an alkylene group having 1 to 10 carbon atoms wherein the carbon atoms may include ether, urethane or ureido linkages therebetween; PA1 each R' is independently selected from hydrogen, monovalent hydrocarbon radicals or halogen substituted monovalent hydrocarbon radicals wherein the hydrocarbon radicals have 1 to 18 carbon atoms which may include ether linkages therebetween; PA1 a is an integer equal to or greater than 1; PA1 each Z is independently a divalent urethane or ureido segment; PA1 each E is independently a polymerizable, ethylenically unsaturated radical. PA1 wherein each A is an hydroxyl or amino radical; PA1 each R is independently selected from an alkylene group having 1 to 10 carbon atoms wherein the carbon atoms may include ether, urethane or ureido linkages therebetween; PA1 each R' is independently selected from hydrogen, monovalent hydrocarbon radicals or halogen substituted monovalent hydrocarbon radicals wherein the hydrocarbon radicals have 1 to 18 carbon atoms which may include ether linkages therebetween, and PA1 a is an integer equal to or greater than 1. PA1 A' is derived from a chain transfer agent and includes a terminal hydroxyl or amino radical; PA1 A" is derived from an ethylenically unsaturated monomer that includes a terminal hydroxyl or amino radical; PA1 cach M' is derived from at least one hydrophilic ethylenically unsaturated monomer, such as the preferred DMA, NOA and/or NVP; PA1 m is an integer of 1 or greater, and preferably 1; and PA1 n is about 5 to 50. PA1 A' in Formula (II) is derived from a chain transfer agent. More specifically, the hydrophilic ethylenically unsaturated monomer M' is polymerized in the presence of the chain transfer agent which serves to control the molecular weight of the resultant polymer and provides hydroxy- or amino- functionality to the resultant polymer. Suitable chain transfer agents include mercapto alcohols (also referred to as hydroxymercaptans) and aminomercaptans. Preferred chain transfer agents include 2-mercaptoethanol and 2-aminoethanethiol. Accordingly, the chain transfer agent forms a terminal end of the hydrophilic polymer, with the hydroxy radical (in the case of a mercapto alcohol) providing the resultant polymer with terminal hydroxyl functionality, and the amino radical (in the case of a aminomercaptan) providing the resultant polymer with terminal amino functionality. Generally, the molar ratio of chain transfer agent to this hydrophilic monomer precursor will be about 1:5 to about 1:100. PA1 A', A" and m are as previously defined; PA1 M.sub.1 is derived from a first hydrophilic ethylenically unsaturated monomer; PA1 M.sub.2 is derived from a second hydrophilic ethylenically unsaturated monomer; PA1 each of n1 and n2 is at least one, and n1+n2 is about 5 to 50. PA1 R.sub.23 is hydrogen or methyl; PA1 each R.sub.24 is hydrogen, an alkyl radical having 1 to 6 carbon atoms, or a --CO--Y--R.sub.26 radical wherein Y is --O--, --S-- or --NH--; PA1 R.sub.25 is a divalent alkylene radical having 1 to 10 carbon atoms; PA1 R.sub.26 is a alkyl radical having 1 to 12 carbon atoms; PA1 Q denotes --CO-- or --OCO--; PA1 X denotes --O-- or --NH--; PA1 Ar denotes an aromatic radical having 6 to 30 carbon atoms; b is 0 to 6; c is 0 or 1; d is 0 or 1; and e is 0 or 1.
x is greater than or equal to 1, y is greater than or equal to 1; and z is greater than or equal to 1; and
The thermosetting polymers and copolymers formed from the prepolymers of this invention are useful in forming thermally stable biomedical devices and lenses.